The present invention concerns an intraocular lens which can be inserted into the eye through a relatively small incision on the order of 2 to 3 mm.
Since the development of the phacoemulsification technique by which a cataract can be removed through a small, 2 to 3 mm incision in the eye, there has existed the possibility of implanting an intraocular lens through such an incision. U.S. Pat. Nos. 4,056,855 and 4,268,921, both to Kelman, describe lenses which could fit through a relatively small incision, however, these and other variations have been limited by the diameter of a functional optic, i.e. the dimension of the lens used in passing and refracting light through the pupil. Until recently, a minimal functional diameter was felt to be 5.5 mm. Most intraocular lenses have a 6.0 mm diameter of the functional optic, and it has been deemed advisable by many to present an even larger optical zone for the overall visual efficiency of the eye.
Presently developed, approved, and time-tested lenses are made of a hard plastic composed of polymethylmethacrylate. Such material is not compressible and thus cannot be placed through an incision smaller than its diameter. Accordingly, other techniques and materials have been explored. For example Kelman has utilized a winged type of construction whereby a round, hard plastic implant can be inserted through a 3 mm incision, after which the round optic is expanded. However, this yields only a 3 mm clear zone centrally bounded by frosted wings on each side of the rectangular central optic.
Recently, Staar Surgical Company and Dr. Thomas Mazocco have initiated clinical trials with a silicone lens which can be folded through a 3 mm incision. U.S. Pat. No. 4,449,257 to Koeniger describes a lens made of hydroxyethylmethacrylate, a hydrogel, which can be inserted through a small incision in the eye and allowed to hydrate and enlarge a predetermined size and power within the eye.
U.S. Pat. No. 4,373,218 to Schachar and U.S. Pat. No. 4,478,596 to Michelson each describe an intraocular lens composed of a fluid-expandable sac which can be inserted in a dry, folded condition through a small incision and then inflated in situ within the eye by an optical fluid. In Michelson, the fluid-expandable sac is formed by a semipermeable sheath. A macromolecule having a size larger than the pores in the sheath are disposed within the sac for setting up an osmotic gradient which draws aqueous humor fluid from the anterior chamber of the eye through the pores of the semipermeable sheath into the sac for inflating the sac to a predetermined shape. In Schachar, on the other hand, the fluid-expandable sac is made of a nonporous material and is inflated in situ with either a liquid or a gas by way of a valve, or tubule, which communicates with the interior of the sac and extends through the sclera of the eye. One of the problems that can develop with the intraocular lens of both Michelson and Schachar is that if the sac should become ruptured, for example as a result of subsequent surgical or laser intervention to disrupt a clouded "secondary cataract" or residual posterior capsule of the natural lens, some or all of the fluid in the sac may be released, altering the optical power of the implanted lens.
U.S. Pat. No. 4,542,542 to Wright describes a method for replacing the lens of an eye which involves removing the natural lens, while retaining the natural lens capsule, and forming a synthetic lens in situ in the eye. This is accomplished by injecting into the natural lens capsule a synthetic lenticular composition which is initially pourable and which undergoes a physical change, in situ, due to a curing action which solidifies the composition. The synthetic composition conforms to the shape of the natural lens capsule and holds its shape upon solidification. Wright thus uses the natural lens capsule as a mold to form a synthetic lens in situ in the eye. Wright suggests that this in situ formation of a lens is an improved alternative to other intraocular lens implants because, among other things, it involves a less traumatic and faster surgical procedure. The use of the natural lens capsule to form the lens according to Wright, however, has the disadvantage that the configuration of the natural lens capsule cannot be changed and it is not possible to adjust the power of the in situ formed lens, although it may accommodate as the natural lens does in youth. Additionally, it is not always possible to remove a cataract without destroying part of the natural lens capsule. In such an instance, a synthetic lens formed according to Wright may not have desirable optical characteristics or be practical.